Local loop unbundling (LLU) allows communications providers (CPs) to provide network services, such as xDSL broadband services, over the physical connection between the telephone exchange and the customer's premises (the so called “local loop”), which is typically owned by an incumbent network operator. In the UK, most local loops are owned by BT. LLU allows ISPs to install their own equipment at telephone exchanges in order to connect customer lines to the ISPs' own networks and services.
Typically, in an LLU scenario, CPs will have their own digital subscriber line access modules (DSLAMs) and other network equipment installed at a telephone exchange. Customer lines coming into the exchange are directed to the CP's equipment instead of that of the network operator.
Under sub-loop unbundling (SLU), CPs can also interconnect with the local access network at a point between the exchange and the customer premises. The connection point is usually the primary connection point (PCP), which is typically a street cabinet. SLU can be used for VDSL services such as fibre to the cabinet (FTTC), where the equipment needs to be much closer to the customer premises.
However, SLU for next generation access (NGA) solutions such as FTTC are expensive to deploy, as there are only a small number of potential customers per cabinet. One solution offered is a bitstream access service, where a CP buys an active connection for a service such as FTTC from the network operator. The network operator owns and operates the DSLAM and other equipment required to provide the service. The CP does not have any direct access to the network infrastructure, as in LLU or SLU solutions, but only has access at the service level.
Under bitstream access, CPs are only given limited control over the services they offer and multiple CPs will offer services to their customers from the same DSLAM. In order to prevent customers being accidently or maliciously reconfigured by a competitor, each CP's circuit must be isolated from the other CPs and choice of DLM (dynamic line management) profile are maintained by the network operator providing the bitstream access service. DLM is a technique used for improving the stability of a DSL line. In most cases, the DLM profile of a customer's line is managed by the network operator and isolated from CP control. The CP therefore only has indirect control of how their customer's line operates via product options, which tend to define the service at a high level, e.g. an “up to xMbps service”.
The limited choices available to the CP are managed via a CP interface into the network operator's OSS/BSS (operational support system/business support system), typically via an XML gateway. The CP is not provided any direct access to the network equipment, or its management platforms. This significantly limits the level of customisation available to a CP in respect of its customers' DSL services, and hence its level of differentiation from other CPs.